I know, the ribbed legs look very tight, but this fits DS-15's slim feet and legs best. Don't ask silly questions about the size, I really don't know. We tried them on his feet as we go! He is very pleased with them and will wear them most in weekends or during the holidays as he needs plain black or charcoal grey socks for school.
I used Opal sock yarn. Don't know what type since the label is missing. DS-12 wants a pair of socks too now, something 'with red'.